The following account of the prior art relates to one of the areas of application of the present invention, hearing aids.
The localization cues for hearing impaired are often degraded (due to the reduced hearing ability as well as due to the configuration of a hearing aid worn by the hearing impaired), meaning a degradation of the ability to decide from which direction a given sound is received. This is annoying and can be dangerous, e.g. in the traffic. The human localization of sound is related to the difference in time of arrival, attenuation, etc. of a sound at the two ears of a person and is e.g. dependent on the direction and distance to the source of the sound, the form and size of the ears, etc. These differences are modelled by the so-called Head-Related Transfer functions (HRTFs). Further, the lack of spectral colouring can make the perception of localization cues more difficult even for monaural hearing aids (i.e. a system with a hearing instrument at only one of the ears).
US 2007/0061026 A1 describes an audio processing system comprising filters adapted for emulating ‘location-critical’ parts of HRTFs with the aim of creating or maintaining localization related audio effects in portable devices, such as cell phones, PDAs, MP3 players, etc.
EP 1 443 798 A2 deals with a hearing device with a behind-the-ear microphone arrangement where beamforming provides for substantially constant amplification independent of direction of arrival of an acoustical signal at a predetermined frequency and provides above such frequency directivity so as to reestablish a head-related-transfer-function of the individual.
US 2007/230729 A1 deals with a hearing aid system comprising a directional microphone system adapted for generating auditory spatial cues. US 2009/0074197 A1 deals with a method of configuring a frequency transposition scheme for transposing a set of received frequencies of an audio signal received by a hearing aid worn by a subject to a transposed set of frequencies.
A problem in particular with behind-the-ear (BTE) hearing aids is that the microphones are placed above/behind the external ear and thus this attenuation of sounds coming from behind disappears. Front-back confusions are a common problem for hearing impaired users of this kind of hearing aids.